Data storage systems may maintain more than one copy of data to protect against losing the data in the event of a failure of any of the data storage components. A secondary copy of data at a remote site is typically used in the event of a failure at the primary site. Secondary copies of the current data contained in the primary site are typically made as the application system is writing new data to a primary site. In some data storage systems the secondary site may contain two or more peer computers operating together as a backup appliance to store the data in one or more storage devices. Each peer computer receives inbound data from the primary site and transfers the data to a storage controller, storage device(s), or other computers for backup storage of the data. This type of system could be used for a disaster recovery solution where a primary storage controller sends data to a backup appliance that, in turn, offloads the transfers to a secondary storage controller at a remote site. In such backup systems, data is typically maintained in volume pairs. A volume pair is comprised of a volume in a primary storage device and a corresponding volume in a secondary storage device that includes an identical copy of the data maintained in the primary volume. Typically, the primary volume of the pair will be maintained in a primary direct access storage device (DASD) and the secondary volume of the pair is maintained in a secondary DASD shadowing the data on the primary DASD. A primary storage controller may be provided to control access to the primary storage and a secondary storage controller may be provided to control access to the secondary storage.
The backup appliance maintains consistent transaction sets, wherein application of all the transactions to the secondary device creates a point-in-time consistency between the primary and secondary devices. For each consistent transaction set, there will be one data structure created that will contain information on all outbound transfers in the set. This structure will be maintained on both of the peer nodes of the backup appliance. The backup appliance will maintain consistent transactions sets while offloading the transactions sets to the secondary device asynchronously. Both peer nodes in the backup appliance may transfer the data to any of the storage devices. To obtain the shortest transfer time it is necessary to divide the data transfers between the peers. An equal division of the data transfers between the two peers may not be optimal because the latency time to transfer data to a particular storage device may be different for each peer. This may result in the first peer finishing before the second peer, resulting in idle time for the first peer. In the case where the first peer finishes offloading transactions earlier than the second peer, it may be beneficial for the first peer node to assist the second peer node to complete the remaining transactions. In addition, the peer nodes should adjust the division of data transfers between the peers to minimize idle time at either peer for the present and future consistent transaction sets.
Prior art systems distribute data movement tasks among multiple queue processors that each have access to a common queue of tasks to execute. Each of the queue processors has a queue of its own work and is able to access each of the other queue processor's queue to submit tasks. This forms a tightly coupled system where every queue processor in the system can access the other queue processor's tasks. Tasks are submitted without any knowledge of the impact on the overall system operation. In certain situations it may not be beneficial to transfer tasks because of overhead costs that may affect the overall system operation. The overhead costs may result in a longer time to complete the task than if the task had not been transferred. In addition the prior art systems do not optimize the operation of the system by adjusting the size of the tasks to transfer. Adjustment of the size of the tasks to transfer is important to react to changing operating conditions that affect the time to transfer data to the storage devices.
There is a need to divide the data transfers between two peer computers to achieve an optimal minimum transfer time to transfer all of the data in a data set and to adjust the division of data transfers to react to varying conditions.